1. Field of the Invention
The present invention relates to an image encoding apparatus for encoding a movement image used for a teleconference or video phone.
2. Description of the Related Art
Generally, in an apparatus for processing image information a data compression circuit is arranged to compress data in order to transfer a movement image having a very large data amount at a low bit rate. The data compression circuit may employ a system of performing different quantization or encoding operations for a still region and a movement region by utilizing the fact that the still portion of an image has a very high inter-frame or inter-field correlation. This system is disclosed in, e.g., Japanese Patent Disclosure (Kokai) No. 61-46685. In the system, input data is divided into a plurality of data blocks by a dividing circuit, and these data blocks are compared with those of an image stored in a frame memory. Thus, a movement of an image is detected by a motion vector detecting circuit. Data blocks of an immediately preceding image are read out from the frame memory, and are input to a variable delay circuit. The variable delay circuit selects one data block from the frame memory which corresponds to motion vector data output from the motion vector detecting circuit. Difference between the data blocks output from the variable delay circuit and input data block is calculated. A movement region detecting circuit discriminates, based on the differential data and the motion vector data, whether or not the input blocks include a movement region.
The differential data is quantized by a quantizer, and is input to a selection circuit. The selection circuit selects one output of the quantizer in accordance with an output from the motion vector detecting circuit. The selected quantized output is input to a variable-length encoder and a local decoder. The variable-length encoder multiplexes the selected quantized output and the motion vector data from the motion vector detecting circuit and outputs multiplexed data. The frame memory is rewritten by the decoded output from the local decoder.
In the system described above, since only a change in inter-frame or inter-field luminance is used for motion vector detection, a man's face, shoulder, chest, background, and the like are equally processed. however, in an actual communication utilizing a moving image, significant data is concentrated on a man's face, in particular, his or her eyes and mouth. If such significant data is equalized with insignificant data, a resultant image is displayed as a stiff image.